The basic philosophy of the F amp is simplicity and minimum amount of stages. It doesn't make any sense if you add a couple of of op amp along the way. So which DAC do you use... and how does it implement its output stage...

I had a TDA1541 at one time too, driving a resistor direct. I too felt it was a bit lethargic. There is no sense of ummph. My guess is the chip itself wants to see a virtual ground at the output, but the voltage will swing because of the passive resistor. Output level tends to be low because there is a limit tot he voltage swing.

You should consider the Pass D1 output stage for your I-V conversion. I think it is probably one of the better implementation for I-V conversion. Better than a op amp I-V converter. Search around this forum for the Pass D1 service manual.

Well the reason, I sound a bit negative towards op amp, is the very nature of op-amp is directly opposite the philosophy of the F series amps. F amps are charaterised by high linearity open loop and minimal or no global feedback with minimal active stages. Op-amps are by their nature, high gain, low linearity open loop and massive global feedback and has about 4 active stages. So putting them in the same bed seems counter intuitive.

However even opamp outputs have varities to them. there are those used with I-V conversion, and/or differential amping filtering and output buffer. There are some with a single op amp stage just for differential output as well some with 4 stages of op amp for i-v conversion, differential output followed by a low pass filter and finally a buffer. This will give it something like 16 transistor gain stages.

Theoretically, it would be possible to power your amp with the DAC chip directly, given the theoretical minimum of 1 transistor (example, F2, Aleph, SIT) in between the DAC chip and the speaker.

However the proof is in the pudding, so it will be worthwhile to hear listening impressions of your DACs with your F-amp.

As for myself, I have not gotten around to rotating different DACs with my F2j yet. So not really qualified to comment.

The basic philosophy of the F amp is simplicity and minimum amount of stages. It doesn't make any sense if you add a couple of of op amp along the way. So which DAC do you use... and how does it implement its output stage...

Oon

Good questions, that's exactly what's on my mind, lately.
Building the best possible DAC in First Watt style.... (nice project for the long upcoming winter)
Hoping on a lot of suggestions here ...

I will for the time being go with the Subbu DAC V3. Inexpensive and simple, basically a ES9023 DAC and a WM8804 receiver. I am hoping there will be an I2S version as I have a nice setup waiting for that too. Looking to upgrade to an ES9018 DAC in the future but that gets expensive and the F5T kinda drained my budget for now!